How to improve the contrast and colors without getting clamping?
You can use the Dodge and Burn nodes for that and they will add a glow effect too on your image.
The dodge node will brighten your image, the burn will darken it. Both have more effect on bright areas and no effect on dark areas, so to avoid clamping we will apply more dodge on the darker parts and more burn at the brighter area, then we will mix them to only have the burn from the dark value of the source image and the dodge from the bright values. If this is not clear here is a step by step.

For this example I will use this source image:



Burn node:

To apply the burn on bright areas, add a Mix node in Burn mode and plug the source image to the 3 inputs. If an area is dark the image used as a factor won't apply the burn so it won't set the value bellow 0.

Dodge node:

For the dodge add a Mix node in Dodge mode then plug the source image to the 3 inputs but this time invert the image for the factor. This is the opposite, the dodge will be mostly applied on the darker value, but at the same time it has less effect on those so you will mostly get the effect on middle gray values, you won't have any clamping.

Blending the nodes:

Now to blend the two images add a Mix node, use the original image as a factor. The first slot will be the image used for everything dark to middle gray and the second for middle gray to bright.
For the first slot connect the Burn mode, to get the slight effect he has added on the shadows, for the second the dodge.

The contrast will probably be too strong, you can add a mix node and plug the original image in the first slot and the image retouched in the second slot. Now use the factor to adjust the contrast, here it is at 0.5: